When I put clay onto the blade I go about half way up the tang in order to leave a section of metal to hold onto with the pliers when I do the heat treatment. When I quench the blade the blade I only dip the section with clay on it into the oil and allow the rest of the tang air cool, thus the tangs of the blades aren't hardened and remain soft.Sorry about the confusion and thanks for pointing it out, I will add in a brief sentence or two to clear this up in the Instructable.

The first picture with step 5 shows when I had just put the clay on and it was still soft. The electronic parts were just used to hold the knives in place and prevent them from tipping sideways. There aren't any electrical processes that need to be done with the heat treatment.

Most alloys nowadays are pretty standard and don't have high levels of impurities, so a standard piece of iron or steel is unlikely to have any lead in it. Lead is a really soft metal so it wouldn't make a good lawn mower blade, it also has a very low melting point so you would be able to tell its lead almost instantly. The main metals to be careful with when doing home metalwork is anything which has been electro-plated with zinc or chrome (looks shiny and is "rust" resistant) as these can give off toxic fumes. That being said never do metalwork indoors as fumes from either the metal or the fire can be toxic in high concentrations.

The egg timer is a silicon/plastic ball the size of an egg which slowly changes colour as it heats up. You place it in the pot with the eggs and when the colour change reaches the desired mark on the red card inside you know how cooked the eggs are.